Apparatus for incorporating additive dispersions to wet webs of paper

ABSTRACT

AN UPHILL APPLICATOR APPARATUS FOR INCORPORATING ADDITIVES TO WET WEBS OF PAPER. THE APPARATUS HAS PARTICULAR UTILITY FOR INCOPROATION OF DISPERSED ADDITIVES TO WET PAPER WEBS CONTAINING PRE-APPLIED FLOCCULENT MATERIALS, AND COMPRISES SUPPORTING FORAMINOUS WIRES, ADDITIVES DISPENSING HEAD BOX MEANS AND VACUUM MEANS FOR CONTROLING THE EXTENT PENETRATION OF THE ADDITIVE DISPERSION INTO THE PAPER WEB.

F. ARLEDTER APPARATUS FOR INCORPORATING ADDITIVE DISPERSIONS Feb. 2, 1971 H.

T0 WET WEBS OF PAPER Original Filed Sept.

HANNS F. ARLEDTER IN VEN TOR.

AGE/VT United States Patent 015cc 3,560,334 Patented Feb. 2, 1971 3,560,334 APPARATUS FOR IN CORPORATING ADDITIVE DISPERSIONS TO WET WEBS OF PAPER Hanns F. Arledter, Chillichothe, Ohio, assignor to The Mead Corporation, Dayton, Ohio, a corporation of Ohio Continuation of application Ser. No. 490,453, Sept. 27, 1965. This application Jan. 27, 1969, Ser. No. 797,357 Int. Cl. D21h 3/00 U.S. Cl. 162-266 2 Claims ABSTRACT OF THE DISCLOSURE An uphill applicator apparatus for incorporating additives to wet webs of paper. The apparatus has particular utility for incorporation of dispersed additives to wet paper webs containing pre-applied flocculent materials, and comprises supporting foraminous wires, additives dispensing head box means and vacuum means for controlling the extent of penetration of the additive dispersion into the paper web.

This application is a continuation of Ser. No. 490,453, filed Sept. 27, 1965, now abandoned.

This invention relates to novel methods for the incorporation of additives in a web of paper, paperboard and the like, and to apparatus therefor.

To adapt a web of paper or paperboard to any one or more of a host of end-use applications, additives of various kinds have been incorporated therein by a variety of prior known methods. Such additives modify the physical and/or chemical properties of the paper or paperboard to enhance such properties as printability, brightness, opacity, permanence, water and/or grease resistance, wet and dry strength, softness, flame resistance, color, chemical reactivity, moldability, extensibility and the like. In the prior art, such additives have been incorporated in the web by either (1), addition to the fiber suspension prior to web formation, or (2), addition to the web following its formation, in either the wet state, after partial drying, or after the web has been substantially dried.

While the art is replete with teachings for adding additives such as mineral fillers, sizes and the like to a wet web during or just following its formation, such prior methods have not found general acceptance in commercial practice.

Various problems are encountered when incorporating additives to a wet web prior to, during or after its formation. When additives are added to the fiber suspension prior to web formation, the problem of retention of the additives becomes of paramount importance. Since paper and/ or paperboard webs are normally formed from very dilute fiber suspensions having a consistency (solid content) of from about 0.01 to 2.0%, large quantities of water are removed at high drainage rates, and such high velocity drainage through a forming network of fibers carries some portion of the additives, present in the fiber suspension, through the forming member or screen. Even when chemical retention aids are used, some portion of the additive is carried away from the forming web in the white water. Furthermore, some kinds of additives added to the fiber suspension adversely affect the strength properties (both wet and dry) of the web.

Other problems are presented when additives are incorporated into the formed web. If this step is carried out after substantial drying, it is often difiicult to achieve uniformity of distribution throughout the thickness of the web where this is desired. And where surface application is desired, many additives will require concurrent use of a substantial amount of an adhesive to hold the additive in place on the web surface. The presence of such adhesive, in many instances, interferes with desired functions of the additive. For example, chemical reactivity may be reduced thereby.

The present invention relates to an improved method for incorporating additives to a wet paper web during or just following its formation. According to this method, a dispersion of the additive is prepared, using a dispersing agent selected to provide a stable, uniform dispersion of the additive. Such dispersing agent is of the type which will interact with a particular fiocculant, said fiocculant being incorporated into the web prior to addition of the additive dispersion thereto.

Accordingly, it is an object of my invention to provide a novel apparatus for incorporating additives to a wet, formed or partially formed web of paper, paperboard and the like, which apparatus enables substantially complete retention of the additive and provides a measure of control of the distribution of the additive throughout the area and thickness of said web.

It is a further object to incorporate flocculants in the Web which coact with dispersants used in preparing dispersions of additives which are subsequently applied, thus inducing controlled flocculation of the additive dispersion upon its contact with the Wet web.

Other objects will become apparent from the description, drawing and examples which follow.

In the drawings, FIG. 1 is a diagrammatic elevation view of the wet end of a Fourdrinier paper machine, and FIG. 2 is a diagrammatic elevation of a device for applying additives to the Wet web, the device being located between the wire section and the press section of a paper machine.

In paper making, fibers are selected which will contribute to the desired physical properties of the finished paper. Most often these are cellulosic in character, and are derived from natural sources such as wood, cotton, hemp, certain grasses such as esparto, and the like. Synthetic organic or inorganic fibers may also be used, including regenerated cellulose (rayon), nylon, polyester, polyvinyl chloride, acrylic, glass, ceramic, and metal fibers of aluminum, nickel, steel, lead and other metals. Natural inorganic fibers such as asbestos may also be used. Frequently, fibers of more than one kind are mixed to achieve a balance of the desired properties.

Such selected fibers or fiber blends are suspended in water, processed by various known refiners such as beaters, jordans and the like, and the suspension then delivered, by the pipe 11 (FIG. 1) to the head box 10 of a paper machine indicated generally by 1. The head-box delivers a stream of the fiber suspension through slice 12 onto a forming element or wire 13 whereby the fibers are deposited as an interfelted mat while the suspending water is removed through the forming element by gravity flow, the action of table rolls 14, wet vacuum boxes 15, dry vacuum boxes 16, and couch vacuum box 20. In the area of initial contact of the stream of fiber suspension with the wire, the suspending water flows through the wire with a high velocity, as the filtering action of the layer of deposited fibers has not become effective. As web formation progresses, the layer of deposited fibers becomes thicker and therefore is a much more efficient filtering medium for the remaining fibers. In the initial forming area, however, such filtering action is almost totally absent, and fine fibers or other small particles present in the fiber suspension are carried through the mesh of the wire by the relatively high velocity stream of water passing therethrough.

If the fiber suspension contains additives in the form of emulsions, pigment particles, colloids and the like, significant amounts are carried away in the water passing through the wire and thereby the amount of such additives retained by the web is reduced. This is true even though 3 chemical flocculants or retention aids are used prior to formation. Although such chemicals increase the amount of material retained in the web, some portion is still car ried away in the water.

Following the wet vacuum boxes and before reaching the dry vacuum boxes 16, the top of the wet web is frequently acted upon by a dandy roll 17. The wire and the wet web on its surface next pass over a guide roll 18 to the couch roll 19, which ordinarily is provided with internal suction box 20. The wet web is transferred to a first press section, generally indicated by 2, after passing over the suction box 20. Wire 13 completes its circuit by passing over rolls 21 to breast roll 22.

After leaving couch roll 19, the web 23 passes under idler roll 24 onto the press felt 25 which carries it through the nip of a pair of cooperating press rolls 26 and 27, the lower one of which has a perforated shell and internal suction box 28. After passing the press nip, the web 23 wraps the surface of roll 26 for a short distance and is then delivered to subsequent parts of the machine (not shown). Press felt 25 is trained in a continuous loop around idler rolls 29 and guide and stretch rolls not shown.

Attempts to overcome the relatively high loss of additives in the initial forming area have involved application of dispersions of additives by such devices as sprays 30, 30 and 30", secondary head box 31, dandy roll applicator 32 or press roll applicator 33. Most often such devices are located at a point where web formation has progressed far enough to provide a filtering action by the fiber layer. Such dispersions of additives have a small particle size, in terms of the pore size in the mat of fibers and/or the mesh size of the wire. Inevitably, some portion of such dispersions is carried through the fiber layer by water still passing through the wire under the influence of the suction devices 15, 16, 2.0 and 28.

According to the present invention, most of the problems of the prior methods are eliminated or greatly reduced in scope and severity. Referring to FIG. 1, a fiocculant is added to the fiber suspension prior to its delivery to the head box 10, or in the head box as indicated at 34, or by sprays 30 to the web in its early stages of formation. Then, a dispersion of the additive is prepared using a dispersant which is selected to interact with the flocculant to cause flocculation of the dispersion. The additive dispersion can be conveniently added to the web by sprays 30', 30", secondary head box 31, dandy roll applicator 32 or press roll applicator 33. Upon contacting the wet web and its contained flocculant, the additive dispersion is caused to flocculate whereby the fine particles of the dispersion aggregate or clump together, thus greatly increasing the effective particle size to a point where this now exceeds the pore size of the forming web. As a consequence, retention of the additive is significantly improved.

It has been found that application of the additive dispersion at a point between the couch roll 19 and first wet press 26, 27 gives particularly good results with a wide variety of additive types. While this may be accomplished by sprays 30" as shown in FIG. 1, the device set forth in FIG. 2 provides a means for handling thin wet webs, without significantly increasing their moisture content, and without disruption of the fiber structure as may happen with spray application of additive dispersions to thin webs.

Referring now to FIG. 2, the device, which may be generally referred to as an uphill applicator is indicated generally by 3. In this device, the wet web carried on wire 13 is transferred to a top wire or fabric 35 as the web reaches couch roll 19. Top wire 35 is trained in a continuous loop around rolls 36, 37, 38, stretch roll pair 39, and guide roll 41. A bottom wire or fabric 42 is trained in a continuous loop around rolls 43, 44, 45, stretch roll arrangement 46, 47, 48, and guide roll 49. Rolls 36, 37 and 43, 44 are positioned so that the web is securely sandwiched between top wire or fabric 35 and bottom wire or fabric 42 throughout the distance from roll 43 to roll 44. A head box is provided with an additive dispersion through feed pipe 51. A portion of the bottom of head box 50 is inclined to lie parallel to top wire 35 as shown at 52. Apron 53, made of 'fiexible material, is arranged so that its free edge lies in sliding engagement with the upper side of top wire 35. Suction boxes 54 are located so that the lower surface of wire or fabric 42 slides across their top surfaces, very much the same as suction box-forming wire relationships on the Fourdrinier part of the paper machine. Material passing into suction boxes 54 is removed through pipe 55.

After passing through the uphill applicator device, the web 23 is transferred to press felt 25 and thereafter may be processed in any desired manner, which may include a second addition of an additive of the same or a different variety at some later step in the process, i.e., at the wet presses, smoothing press, size press, calender stack or the like.

In operation, with use of the uphill applicator device, an additive dispersion is supplied to head box 50 by means of supply pipe 51. The level of dispersion in head box 50 is maintained at a constant level, either by regulating the supply through pipe 51, or by a constant level-overflow arrangement (not shown) as is well-known in the art. The additive dispersion flows over apron 53 onto wire or fabric 35 and is caused to pass therethrough and into web 23. The vacuum applied to suction boxes 54 may be adjusted to any desired value, but suitably is sutficient to insure complete penetration of the wet web by the additive dispersion. Excess dispersion passing through the web and into suction boxes 54 and leaving the device through pipe 55 may be adjusted to the desired concentration with fresh additive dispersion and recycled, so that losses of the additive are substantially eliminated. Incorporation of the additive in the web at this location, immediately following the Fourdrinier part of the paper machine, has a number of advantages. First, most of the free water (i.e., the water removable by the action of suction boxes) has already been removed. Furthermore, the watercontent of the web leaving the applicator device is not adversely increased by the water present in the additive dispersion. Thus, there is no abnormal water-removal required of the wet press section of the paper machine, as is the case when additive addition is carried out by such devices as sprays 30 or press roll applicator 33. Operation of the device is easily controlied by control of the solids concentration of the additive dispersion, the level maintained in head box 50, and the vacuum applied to suction boxes 54. Likewise, the kind and amount of fiocculant added to the web prior to the addition of the additive dispersion and the kind and amount of dispersing agent used in preparing the additive dispersion will aid in controlling the distrbution of the addtive in the web by control of the size of the flocs which result from the interaction of the flocculant with the dispersing agent. When a predominantly surface application of additive is desired, a flocculant and a dispersing agent are selected and used in concentrations which favor the formation of relatively large flocs of the additive, and operations are carried out with minimum vacuum applied to suction boxes 54. Conversely, when more uniform distribution of the additive throughout the thickness of the web is desired, the flocculant and dispersing agent, and the concentrations thereof are selected to favor the formation of relatively small flocs, and the vacuum applied at suction boxes 54 is adjusted to a level whereby the relatively small fiocs are carried into and distributed throughout the web.

EXAMPLE There was prepared an additive dispersion comprising an anionic sol of cooked potato starch at a solids concentration of 1%. Flocculants were added to the papermachine head box in an amount to give 0.01% polyethylene oxide and 0.05% polyethylene imine, based on dry fiber Example Control Starch added, percent... 1. 25 0 Burst, p.s.i. 54 34 M.I.T. fold (No.)... 363 70 Tensile, gm./iu 20, 700 14, 200

The 0.01% polyethylene oxide and 0.05% of polyethylene imine added to the head box, interact with the fibers in the stock suspension to cause fluocculation thereof, whereby drainage on the wire is improved, and fine fibers better retained in the wet web. The polyethylene imine is present in excess, and is available in the web to cause flocculation of the starch sol.

What is claimed is:

1. Apparatus for incorporating additive dispersions to wet webs of paper following formation thereof comprismg (A) means for transporting a wet web in a general upward direction while sandwiched between upper and lower foraminous wires,

(B) head box means positioned above said upper foraminous wire at a point Where said upper foraminous wire is in contact with said wet web for supplying a flow of additive dispersion through said upper foraminous wire and into said upwardly traveling web, and

(C) vacuum means positioned generally opposite said head box means and in contact with the lower side of said lower foraminous wire for providing penetration of said wet web by said additive dispersion and for receiving that part of said additive dispersion passing through said wet Web.

2. The apparatus of claim 1 additionally having means associated with said vacuum means to recycle that part of said additive dispersion received by said vacuum means.

References Cited UNITED STATES PATENTS 1,914,526 6/1933 Rafton 162184X 1,922,325 8/1933 Rafton 162-180 2,111,440 3/1938 Strasser 162266 3,250,665 5/1966 Gess 162-185X 3,279,975 10/1966 Yosall 162185X 3,384,536 5/1968 Sandberg 162186 S. LEON BASHORE, Primary Examiner R. H. ANDERSON, Assistant Examiner US. Cl. X.R. 

